Drug delivery devices allowing for multiple dosing of a required dosage of a liquid medicinal product, such as liquid drugs, and further providing administration of the liquid to a patient, are as such well-known in the art. Generally, such devices have substantially the same purpose as that of an ordinary syringe.
Pen-type injectors of this kind have to meet a number of user specific requirements. For instance in case of those with diabetes, many users will be physically infirm and may also have impaired vision. Therefore, these devices need to be robust in construction, yet easy to use, both in terms of the manipulation of the parts and understanding by a user of its operation. Further, the dose setting must be easy and unambiguous and where the device is to be disposable rather than reusable, the device should be inexpensive to manufacture and easy to dispose. In order to meet these requirements, the number of parts and steps required to assemble the device and an overall number of material types the device is made from have to be kept to a minimum.
There exist various training cartridges or syringes to be operably coupled with a drive mechanism of a drug delivery device. When appropriately coupled with the drive mechanism, known training cartridges should provide a realistic feedback to the user on how the drug delivery device and its mechanical components behave during dose setting and dose dispensing procedures. In a simple approach, training cartridges are filled with water or a placebo featuring comparable mechanical properties to the genuine medicinal product originally contained in the cartridge of the same or similar type. Even though such water- or placebo-filled cartridges may provide realistic mechanical feedback of the cartridge itself and for the drug device's drive mechanism and also mimic the visible behaviour of the cartridge, such dummy cartridges might be accidentally confused with genuine cartridges filled with a medicinal product. Consequently, the patient may inject water or placebo instead of the prescribed drug and may thus be treated with an incorrect amount of medicinal product.
Furthermore, when making use of water- or placebo-filled cartridges, any of such training or dummy cartridges must be sterile filled or terminally sterilized in case the contents are injected. This also means that the training or dummy cartridge can only be injected by a single user in order to prevent any potential contamination of the cartridge, e.g. in case the cartridge would be used by several users. Moreover, such water- or placebo-filled cartridges have to be used up within a given shelf life or within their given in-use life.
Alternatively, the water- or placebo-filled cartridges may be used for training purposes without injection of the cartridge contents, for example the user dispenses the cartridge contents into an injection pad or into a container. Although this approach has certain advantages, it does not allow the user to practice the step of needle insertion into the skin. A user may suffer from needle phobia or needle anxiety and find that he is unable to insert the needle into the skin. Furthermore, a user who can insert the needle, but who has limited dexterity or strength, may find that he is unable to dispense the device with the needle inserted, for example due to the particular position that the device must be held in during the injection or due to additional pain caused by an unsteady hand moving the needle during the injection. If needle insertion and completing the dispensing action whilst the needle is inserted form a part of the device training process then the healthcare professional can make a proper assessment of the users' capability and take appropriate action.
With these water- or placebo-filled cartridges it is further disadvantageous, that after discharging, the entire cartridge has to be replaced by a new water- or placebo-filled cartridge. Such single-use disposable liquid-filled training cartridges therefore require a corresponding supply and waste management comparable cartridges filled with a liquid drug.
Other approaches suggest to train the device handling without a cartridge assembled therein. However, this is considered to be generally inadequate for the purpose of providing reasonable visual or tactile feedback to the user. First of all, the user does not receive any mechanical and/or otherwise perceptible feedback typically originating from the cartridge. The injection force as well as the length of injection cannot be appropriately simulated. Also, this method lacks a visual feedback on the axial movement of the cartridge's piston. Additionally, a cartridge substitution or cartridge replacement cannot be simulated. Furthermore, needle attachment and the puncturing of the cartridge's septum by means of an injection needle is not trainable in the absence of a cartridge.
It is therefore an object of the present invention to provide a training or test cartridge for a drug delivery device that simulates the overall behavior of a genuine cartridge to a large extent. Preferably, the training cartridge does not require filling with water or a placebo. It is a further aim of the invention, to provide a training cartridge to be usable by numerous users and which is restorable to its initial configuration. Moreover, the invention focuses on a method of resetting a training cartridge for a drug delivery device and further aims to provide a drug delivery device equipped with such a training cartridge.